Cerebrospinal fluid norepinephrine concentrations were preoperatively determined in five patients. Stereotaxic thalamotomy was performed using depth coagulating electrodes. No significant alterations in prestimulation lumbar cerebrospinal fluid norepinephrine levels were noted twelve days after electrode installation. Twelve hours after intermittent electrical stimulation of the caudate nucleus, lumbar cerebrospinal norepinephrine concentration was significantly decreased suggesting stimulation-induced inhibition of noradrenergic pathways. In nine Huntingtonian patients with caudate atrophy norepinephrine levels were significantly lower than those noted in nine age-and sex-matched control patients.